This invention relates to a railroad sleeper formed from steel which is useful for maintaining the gauge of rails.
Various configurations have been proposed in the past for retaining rail gauge in a railroad, including the formation of depressions in the upper surface of a sleeper, the location of apertures in a sleeper, and other configurations. It has also been proposed to maintain gauge by a stud welding process.
This invention seeks to provide a rugged steel sleeper which is capable of maintaining gauge, and which can be used in conjunction with a simple spring type retaining clip (for example in accordance with our U.S. patent application Ser. No. 366,655 filed Apr. 8, 1982), and which can also be utilised with insulation pads.
If a railroad sleeper is provided with depressions in its upper surface, those depressions must be formed against the rigidity of the upstanding walls and this requires tremendous forces and therefore large presses. Furthermore, reduction of section modulus results in loss of strength. Alternatively, if use is made of apertures in a sleeper, the apertures constitute weakness zones having high stress concentration points, and these are regarded with considerable disfavour. These problems have been largely solved by a previous invention of ours making use of a stud welding process, but the stud welding process requires jigging to achieve accuracy of positioning. The cross sectional shape and size of a weld stud is extremely limited. Therefore the surface area available for the rail foot to abut is minimal providing little resistance to sleeper "skewing" and also limited resistance to wear.
Another object of this invention is to provide a very simple sleeper which by it configuration will retain gauge and yet which will not be excessively expensive to produce.
When a railroad sleeper is loaded by a vehicle passing over rails supported by the sleeper, the metal stresses at the localities of the rails include a vector addition of longitudinal stresses along the sleeper and transverse stresses across the sleeper, and in some instances these stresses are subject to reversal. These stresses are greatest at the top of the sleeper and are critical at the rail localities. However, it is adjacent the rails that the studs are welded, and it is inherent in a welding process of any fastening system to a steel rail that residual stresses remain in the rail adjacent the weld metal, and this can in some instances result in fatigue cracking. The danger of fatigue cracking is increased in those localities wherein the residual welding stresses are additive to the live load stresses.
Another object of the invention is to provide a sleeper which by its configuration increases the section modulus at the localities where fastening systems are welded, thereby proportionately reducing live load stresses.
If a sleeper has a constant cross-sectional shape throughout its length, there is a relationship between the bending moment and the distance along the sleeper from the rail, the maximum bending moment being at the locality of the rail. It is a further object of this invention to provide a sleeper which by its shape moves the critical area of the sleeper logitudinally along the sleeper to a locality of reduced bending moment for some at least of the anticipated applied loads.